1. Field of the Invention
This invention relates to a solid state laser, and more particularly to a solid state laser in which a pair of .lambda./4 plates are disposed in a resonator to make an oscillation beam of a twisted mode. This invention further relates a method of manufacturing such a solid state laser.
2. Description of the Related Art
There has been known, as disclosed for instance in Japanese Unexamined Patent Publication No. 62(1987)-189783, a solid state laser in which a solid laser rod doped with rare earth metal such as neodymium is pumped by a semiconductor laser (laser diode).
In such a solid state laser, it has been proposed to dispose a pair of .lambda./4 plates in the resonator to make an oscillation beam of a twisted mode (elliptically polarized mode) between the .lambda./4 plates, thereby making the oscillation mode of a single longitudinal mode.
Further as disclosed in U.S. Pat. No. 5,671,240, a polarization control element such as a Brewster plate is often provided in a resonator in a solid state laser of the type in which an oscillation beam is made of a twisted mode, thereby setting the linear polarization of the solid state laser beam in a predetermined orientation.
There has been a problem in conventional solid state lasers of the type in which an oscillation beam is made of a twisted mode that the resonator loss is large and accordingly it is difficult for the solid state laser to operate at a high power.